Propositions and Same-Saying: Introduction Philosophers often talk about the things we say, or believe, or think, or mean. The things are often called ‘propositions’. A proposition is what one believes, or thinks, or means when one believes, thinks, or means something. Talk about propositions is ubiquitous when philosophers turn their gaze to language, meaning and thought. But what are propositions? Is there a single class of things that serve as the objects of belief, the bearers of truth, and the meanings of utterances? How do our utterances express propositions? Under what conditions do two speakers say the same thing, and what (if anything) does this tell us about the nature of propositions? There is no consensus on these questions—or even on whether propositions should be treated as things at all. During the second Propositions and Same-Saying workshop, which took place on July 19–21 2010 at the University of Sydney, philosophers debated these (and related) questions. The workshop covered topics in the philoso- phy of language, perception, and metaphysics. The present volume contains revised and expanded versions of the papers presented at the workshop. 1. Background The participants in this workshop shared the working assumption that there are propositions. Before delving into a discussion of what propositions are and what they do, it is worth establishing a prima facie case that there are such things. Some arguments against the existence of propositions—most notably the ones advanced by (Quine, 1960; Quine, 1969; Quine, 1951)—appeal to gen- eral skeptical principles. Nominalists ask: why believe in spooky, abstract propositions when we can get by with eternal sentences—or perhaps even token utterances of sentences? Skeptics about the intensional ask: can we really make sense of analyticity, synonymy, meaning—or proposition—even though none of these is definable in terms of any of the others? Defenders of the slogan ‘no entity without identity’ insist that until we have a method for discovering when two sentences express the same proposition, we have no business talking about propositions at all. These skeptical considerations, however, are at odds with sound linguis- tic and philosophical practise. Compositional semantics assigns functions to each syntactic unit, so that well-formed sentences are assigned propositions— construed as functions from (e.g.) worlds (or ‘circumstances’) to truth-values. c 2011 Kluwer Academic Publishers. Printed in the Netherlands. INTRODUCTION.tex; 22/03/2011; 22:01; p.1 2 Furthermore, accounts of belief, knowledge, and metaphysical necessity typ- ically assume that these operators all operate on propositions. The debate is not so much whether such things exist, but what the inputs to such functions are. At any rate, it is not clear that propositions must violate skeptical princi- ples. Numerous theories purport to give accounts of when two propositions express the same proposition. Furthermore, the modal realism of (Lewis, 1986) gives a theory of propositions that is extensional and, to a large degree, nominalistically acceptable. For Lewis, all possible worlds are equally real, so intensional constructions (‘it is possible that . ’) can be replaced with the extensional (‘there is a possible world such that . ’). Propositions are then sets of possible worlds. Thus for Lewis, propositions are set-theoretic constructions out of extensional entities, with which even Quine should be happy. Participants in this workshop worked from the shared assumptions that skeptical challenges can be met, that there are such things as propositions, and that it is worthwhile to investigate their nature. 2. Issues In this section, we introduce some of the more specific issues raised in the papers in this collection, and the background to them. 2.1. What kind of entities are propositions? Given that there are propositions, what are they? In particular, what is their granularity—that is, how should we determine when two sentences express the same proposition? Options range from the very fine-grained, on which distinct sentences never express the same proposition, to the very coarse- grained, on which any two sentences with the same truth value express the same proposition. Intermediate options include: S 1 and S 2 express the same proposition whenever they are metaphysically equivalent, whenever they are logically or a priori equivalent, whenever they are equivalent and identical in syntactic structure, whenever they are equivalent and about the same topic, or whenever they share the same set of potential truthmakers. The ‘possible worlds’ approach to granularity, exemplified by (Stalnaker, 1976b; Stalnaker, 1976a), equates each propositions with the set of possibil- ities at which it is true. And advantage of the possible worlds approach is its ability to capture numerous modal and semantic relations among propo- sitions. For instance, the possible worlds approach holds that A entails B whenever A is a subset of B, A is possible whenever A is non-empty, and A and B are incompatible whenever their intersection is empty. INTRODUCTION.tex; 22/03/2011; 22:01; p.2 3 Many critics of the possible worlds approach, including Rabern, Weber, Jago, and Ripley in this volume, adopt hyperintensional approaches, on which distinct propositions can be true in all the same possible worlds. One com- mon argument for hyperintensional approaches is as follows: It seems that someone could believe the proposition expressed by ‘Samuel Clemens had a moustache’ without believing the proposition expressed by ‘Mark Twain had a moustache’, even though these propositions are necessarily equivalent. Since necessarily equivalent propositions can have different properties (for instance, one can be believed by Alice, while the other is not) it follows that they are distinct entities. Hyperintensional approaches can be divided into two camps. The ‘struc- tured entities’ approach, exemplified by (Soames 1987), treats propositions as structured aggregates of semantically significant parts. According to ‘Russel- lian’ versions of the approach, the semantically significant parts include prop- erties and entities—so that, for instance, the proposition that Fred is happy is a structured aggregate composed of Fred himself and the property happiness. In this volume Kit Fine argues that a structured entities approach propositions captures features of counterfactual reasoning that a possible worlds approach cannot. Since propositions with the same truth conditions embed differently in counterfactuals, he argues, we should replace possible worlds approaches with approaches that discriminate more finely on the basis of propositional structure. The second, ‘circumstantialist’ approach, exemplified by Lycan (1997) and Nolan (2000) holds that propositions are sets of possible and impossible worlds. (Some authors use ‘circumstances’ to encompass both possible and impossible worlds.) In this volume, Mark Jago discusses a way of construct- ing circumstances within an actualist framework, according to which all that is exists is what actually exists. Dave Ripley argues for the circumstantialist approach over the possible worlds approach. 2.2. What Roles Do Propositions Play? Many of the debates about propositions concern not what they are but what they do. In contemporary philosophy, the term ‘proposition’ is often used to talk about the things that are (in the first instance) true or false (the ‘primary’ bearers of truth and falsity); the objects of belief, desire and other psycho- logical (or ‘propositional’) attitudes; the the referents of ‘that’-clauses; the bearers of alethic modal properties (being possible and being necessary); and the relata of the various entailment relations. Propositions are also often said to be the semantic content, meaning or compositional semantic values of declarative utterances or sentences; or what is said in making such utterances. Given so many theoretical roles associated with the term ‘proposition’, it is hardly surprising that philosophers are sometimes unsure exactly what INTRODUCTION.tex; 22/03/2011; 22:01; p.3 4 propositions are. David Lewis, for example, says that ‘the conception we associate with the word ‘proposition’ may be something of a jumble of con- flicting desiderata’ (1986, 54). One task for the philosophy of propositions, therefore, is to clarify each of these theoretical roles and to assess whether any single kind of entity can play them all, or even most of them, simultaneously. In this volume, Weber and Rabern discuss propositional multitasking, the idea that (some notion of proposition) can play all or most of these roles. Here, we’ll say a little about each of the roles commonly associated with the term ‘proposition’ in the literature, and indicate a few of the points of potential conflict between them. Bearers of truth and falsity: Many philosophers argue that propositions are the primary bearers of truth and falsity. This is not to deny that other entities or events—utterances, sentences, beliefs etc.—are also capable of being true or false. But, by saying that propositions are the primary bearers of truth or falsity, one is saying that the truth or falsity of an utterance or belief depends on the truth or falsity of the proposition expressed by that utterance or on the proposition believed (what is believed). Here is a version of the argument for taking propositions to be the primary bearers of truth and falsity, formulated in terms of belief. We can distinguish between a specific act of believing (a specific mental state or event) and what is thereby believed. Whether that belief is true or false depends only on what is believed. It does not depend, for example, on the particular neural realisa- tion of that mental state or event (unless the belief happens to be one about its own particular realisation—but then, this is reflected in the proposition that captures what is believed). Assuming that what is believed is a proposition, we can explain the truth or falsity of a particular belief in terms of the truth or falsity of the proposition believed. The story is similar in the case of the truth or falsity of particular utter- ances.